Recent estimations indicate that, on the average, various aircraft in the U.S. commercial aircraft fleet encounter lightning discharges about once each year. The aircraft generally encounters the lightning discharge when flying through a charged portion of a cloud. In such cases, the discharge generally attaches to the aircraft and extends outwardly from the aircraft. While the discharge is occurring, it generally moves from the nose of the aircraft and onto a plurality of skin panel portions of the aircraft as the aircraft moves through the charged region. The discharge may also attach to wing tips and/or edges of wing control surfaces (e.g., ailerons) during the discharge. The discharge then generally leaves the aircraft structure through the empennage. Since commercial aircraft include electronic equipment such as navigational computers and communications equipment that may be degraded by a lightning discharge, commercial aircraft comply with a comprehensive set of certification procedures in order to verify that the aircraft is sufficiently protected from the effects of a lightning discharge.
Meanwhile, today's aircraft are being designed and built with greater percentages of composite material. Although composites possess high strength to weight ratios and may have better mechanical and fatigue properties than traditional aluminum alloys, they are less electrically conductive, and offer somewhat less electromagnetic shielding than the metallic materials which they replace, causing somewhat less current dissipation from aircraft. Without a conductive path, arcing and stored voltage (capacitance) can occur that might degrade affected portions of the aircraft structure. For example, lightning may attach to a fastener and then flow though the fastener into a sub-structure below the surface (or skin) of the aircraft. Thus, techniques are implemented to provide conductive paths from portions of these aircraft including the fasteners.
Techniques to improve an airframe's tolerance of electrical charges, particularly when the electrical charges attach to aircraft fasteners, have utility and may improve the economy and/or safety of air transit.